Since the decisive outcome of the campaigns in France and the Low Countries left the British Army considerably inferior to the German Army in strength and materiel, the British had no choice but to avoid full-scale fighting until new power could be marshalled. Accordingly, shortly after the withdrawal from Dunkirk in June 1940, the Imperial General Staff organized a Special Service Brigade under the control of the Director of Combined Operations, Admiral of the Fleet Sir Roger Keyes, who had learned the technique of coastal raids in the First World War. The Brigade was composed of raiding parties and task forces — roving hit-and-run fighters — and soon came to be known as 'commandos' after a Dutch word, derived from the Portuguese, that had come into familiar use in the Boer War as a term describing any military body as well as a raiding party. Under Sir Roger the commandos carried out several 'pin-prick' raids on the French coast and a larger raid on the Lofoten Islands in Norway, in which they developed their peculiar tactics.

Source:

Military Intelligence Service - War Department - U.S. Army - U.S. Goverment